A non-canonical role for EZH2 in rRNA methtlation

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Background: Mounting evidence suggests that dysregulated epigenetic modifications play a crucial role in cancer initiation, progression, and metastasis. Epigenetic regulations include histone modifications, DNA methylation and demethylation, regulations through microRNA and long non-coding RNAs (lncRNAs), and RNA methylation and editing. RNA methylation occurs on all messenger RNA (mRNA), transfer RNA (tRNA) and ribosome RNA (rRNA). Compared to the recent advances in understanding mRNA methylation, the function of rRNA methylation is understudied. The epigenetic modifier Polycomb group protein EZH2, a well-known oncogenic histone lysine methyltransferase for H3K27 methylation and a key component of Polycomb Repressive Complex 2 (PRC2), is upregulated in cancer and is a biomarker of aggressive cancers. Our preliminary data show that EZH2 directly interacts with FBL (Fibrillarin), the only characterized rRNA 2’-O-ribose methyltransferase, and regulates rRNA 2’-O-methylation levels. Knocking down EZH2 alters FBL-mediated nascent peptide synthesis, IRES-driven protein translation initiation, and other ribosomal functions. Importantly, our data reveal that FBL is upregulated in PCa, and EZH2highFBLhigh PCa patients had worse clinic outcomes compared to other patients. Objective/Hypothesis: Our overall hypotheses are that EZH2 plays dual roles in PCa, a canonical role as histone methyltransferase and a non-canonical role by directly interacting with FBL and then regulating rRNA methylation and ribosomal functions. Further, this novel EZH2 function is independent of the PRC2 complex and its lysine methyltransferase activity. Overexpression of EZH2 and FBL together will promote PCa progression. Based on our preliminary data, we propose the following specific aims to test our hypotheses. Specific Aim 1: To investigate how EZH2 regulates the assembly of box C/D snoRNP. Specific Aim 2: To characterize the non-canonical functions of EZH2 in rRNA methylation and protein synthesis through its interaction with FBL in vitro. Specific Aim 3: To examine the EZH2-FBL interaction and EZH2’s novel functions in vivo. Impact: This work will dissect how EZH2 performs its dual role in cancer progression through its canonical function as a H3K27 methyltransferase and a non-canonical function in rRNA methylation via FBL.